Our primary objective is to gain a thorough understanding of the relation of simian virus 40 (SV40) chromatin structure to its function as a template for transcription and replication. We have previously shown that the intracellular SV40 chromatin is heterogeneous with respect to its ability to function as a template, with recently replicated ("new") viral DNA serving perferentially. We are examining the possibility that an interaction with capsid protein(s) is responsible for the diminished template activity. A comparison of the structures of "new" and "old" viral chromatin is being made with the use of various nucleases. We have recently shown that histone-deficient SV40 chromatin cannot replicate without the prior and/or concommitant addition of histones. Further studies will be aimed at understanding the basis of the requirement for histones in viral replication.